The invention relates to a method for manufacturing a coagulation assay device by a continuous process, and to an apparatus for dispensing a reagent containing solution into a plurality of side by side depressions in a ribbon-like flat web.
U.S. Pat. No. 4,849,380 discloses a device for performing an assay by using capillary action to draw a predetermined volume of a liquid sample into a reaction chamber charged with a reagent, where the reaction between the liquid sample and the reagent is monitored. The device includes a base, a spacer having an aperture therethrough laminated against the base, and a cover having a pair of apertures therethrough laminated against the cover to form a chamber having an application port and a vent. After treatment to make the chamber hydrophillic, reagent supplied to the application port by pipette is drawn into the chamber by capillary action and then freeze dried or air dried at room temperature. The thickness of the spacer is critical in order to assure capillary action, and to assure that the chamber has a predetermined volume so that the reagent therein has a predetermined concentration.
The device of U.S. Pat. No. 4,849,380 is especially suitable for a coagulation assay wherein the reaction chamber contains a coagulation reagent such as thromboplastin and inert magnetic particles such as magnetite suspended in the reagent. When a sample of blood or plasma is introduced into the chamber, the dry reagent is solubilized, the magnetic particles settle, and a coagulation reaction is initiated. When an alternating magnetic field is applied, the orientation of magnetic particles changes synchronously with the field; this effect can be monitored optically by changes in intensity of reflected light (flickering). Peak to peak values of light intensity fall off when a clot has started to form, providing a convenient assay for coagulation. Refinements in the method for monitoring the clotting time are disclosed in U.S. Pat. No. 5,110,727 and PCT International Publication No. WO 92/01065.
The processes used to manufacture the known assay device are batch processes which require wetting the reaction chamber with detergent, blowing it out, applying an aqueous reagent solution to the application hole with a pipette, then lyophilizing, i.e., rapid freezing followed by dehydration in the frozen state under high vacuum. This is especially time consuming and not convenient to high throughput manufacturing. However, the possibility of a continuous strip process has not been suggested due to the problem of drying reagent solution in the reaction chambers. Further, magnetic particles must be uniformly dispersed in the reaction chamber to facilitate optical monitoring of the fluctuations between bright and dim reflected light. This is rendered difficult by the tendency of the magnetic particles to settle out prior to application, and further by their tendency to flow toward the vent hole when resuspended by the sample as it is introduced to the chamber. This tendency also mitigates against applying the magnetic particles and the thromboplastin in a two step process.
U.S. Ser. No. 08/114,579, filed Aug. 31, 1993 and incorporated herein by reference, discloses an improved carrier solution for the magnetic particles. This solution lends itself especially to air drying and is resoluble as readily as freeze dried materials. At the same time, the aforementioned tendency of the magnetic particles to aggregate in the sample is avoided. However an efficient method of applying the particle containing solution to the assay devices in a continuous process is not disclosed.